Life cycle assessment of rice husk-based bioethanol production in Uruguay

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Main Presenter:    Camila Alejandra Bacquerié Vagnoni 

Co-Authors:   Valeria Larnaudie     Goycoechea Nicolás                                          

The rice industry generates large amounts of rice husk, a lignocellulosic residue that remains environmentally and economically challenging to manage [1]. In Uruguay, rice husk represents a significant biomass stream with limited valorization pathways [2][3]. Converting this residue into second-generation bioethanol, combined with energy co-production, may contribute to climate change mitigation and improved resource efficiency [4]. In this context, life cycle assessment (LCA) is a key tool to support innovation by identifying environmental hotspots and guiding process optimization.
The objective of this study is to evaluate the environmental performance of a rice husk-based biorefinery for fuel ethanol production under Uruguayan conditions, identifying the main contributors to environmental impacts and improvement opportunities along the life cycle.

An attributional LCA was conducted in accordance with ISO 14040/14044 standards. The functional unit was defined as 1 kg of anhydrous ethanol (99.6%) at the plant gate. System boundaries were set from cradle to gate, considering rice husk transport, processing, and on-site cogeneration of heat and electricity. Rice husk was treated as an agricultural residue with no upstream environmental burdens. The background system was modeled using ecoinvent v3.11 within openLCA software, and environmental impacts were assessed using the ReCiPe 2016 Midpoint (H) method. The analyzed impact categories were climate change, fossil resource use, water use, terrestrial acidification, terrestrial eutrophication, and human non-carcinogenic toxicity. Sensitivity analyses were performed on energy demand, transport distance, and alternative assumptions regarding burden allocation to rice cultivation.

Results indicate that steam consumption is the dominant contributor across all evaluated impact categories, mainly due to biomass combustion and associated logistics. Acid production and raw material transport were identified as secondary contributors, while ash disposal significantly affected human toxicity indicators. Climate change impacts were found to be lower than those reported for first-generation bioethanol pathways, particularly when rice husk is considered a true residue. The sensitivity analysis showed that transport distance did not have a significant effect on the impact indicators assessed. In contrast, allocating a portion of the environmental impacts of rice cultivation to rice husks led to a substantial increase in the impact associated with water use compared to the reference scenario.
This work highlights the environmental potential of rice husk valorization within a biorefinery framework and underlines the critical role of energy efficiency and residue management in improving sustainability. The findings provide decision-support insights for the development of low-impact biofuel systems based on agricultural residues in emerging bioeconomies.

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